Furnace door construction



Sept 3, 1957 H. L. BERGMAN 2,804,855

FURNACE nooR CONSTRUCTION Filed Feb. 2s, 1952 /3 /0 /2 L l 9J Ilg1 o v Z4 5 M Ll I l 53 9 l' /f 36 l C 8 I 2/ f H///i' 4 5 5 *`Z6 7 W 42 44'/ n "I 5 12| 12g k 1 /f l' fag U (gl-Ln 3 INVENTOR T192. 34 55 hiLely/f/an BY rl A L: 1

FURNACE DOOR CONSTRUCTION Herbert Lincoln Bergman, Grosse Isle, Mich., assign-or to Surface Combustion Corporation, Toledo, Ohio, a corporation of Ohio Application February 23, 1952, Serial No. 273,055 Claims. (Cl. 122-498) This invention relates to furnaces, and more particularly to a door construction for furnaces which is especially useful in controlled atmosphere type furnaces and where a furnace door and a frame therefor are internally cooled.

In an effort to maintain a tight sealing door for an atmosphere furnace it is known to internally cool the door and also the frame against which the door must close, the door also being refractory lined to reduce heat losses from the furnace and to keep the metal mating surfaces of the door and the frame somewhat cooler. it is thus known to provide an internally cooled frame at a furnace opening, and to supply a door outside the opening which closes the opening by seating on the frame. It is also known to enclose such a door into a vestibule and to provide as a part of the vestibule a casing into which the door move when opened, thus avoiding direct contamination of the furnace atmosphere by atmospheric air upon opening the door within the vestibule. The present invention provides an improved construction which reduces yet further heat losses through, or to, the door structure when closed, thus reducing warpage, wear and maintenance, and which also reduces the effective volume of the vestibule which must be purged to remove air therefrom before the subject inner door is opened.

For a consideration of what I believe to be novel and my invention, attention is directed to the following portion of the specification and the drawing and concluding claims thereof.

In the drawing:

Fig. l shows a somewhat schematic elevational view of a furnace to which the subject invention is applied.

Fig. 2 shows a vertical sectional view of the charge end of the furnace of Fig. l.

Fig. 3 shows an alternate form of the invention as shown in Fig. 2.

Fig. 4 shows a partial vertical cross sectional view of Fig. 2 taken on line 4 4 thereof.

According to the invention apparatus is provided in which a refractory lined door having a metal rim may close against a frame of a furnace in such a manner as to interpose the lining of the furnace door between the rim and frame and the furnace chamber thus shielding the metal parts from the heat of the furnace when in a closed position. In its preferred form the apparatus comprises, in combination, wall means forming a refractory lined and gas-tight furnace chamber having an access opening therethrough, an internally cooled door frame surrounding said opening and sealed gas-tight to said wall means, and a refractory lined door for closing said opening which has an internally cooled metal rim adapted to seat against said frame with said lining interposed between said rim and furnace chamber when the door is in a closed position.

The furnace comprises a heating portion or chamber 10, a charge vestibule 11 and a discharge end 12, shown in broken lines, which may be a discharge vestibule substantially identical to the charge vestibule, or may be a nited States Patent fie Y, 2,804,855 Patented Sept. 3, 1957 portion of a cooling zone of the furnace as the case may require.

The heating chamber 10 is formed by a metal framework 9 and binding or casing 13, which may be made gas tight, and a refractory lining 14. Heat is supplied by internally fired radiant tubes 15 to avoid contamination of the furnace atmosphere by products of combustion. Work W is loaded into trays or baskets 16 and pushed through the furnace on rollers 17 supported in the furnace on shafts 18.

The charge vestibule 11 is provided with an outer vestibule door 21 and an inner door 22 for the heating chamber. The outer door 21 is raised and lowered by an automatic mechanism 23 mounted on the furnace framework 9, and the inner door is raised by tubular members 24, cross bar 25, and mechanism, not shown, for moving cables 26. The inner door 22 comprises a water-cooled door rim 27 and `a refractory lining 28. Water for internally cooling the door rim 27 is supplied and exhausted through flexible hoses 31 and the tubular members 24. The frame 32 against which the watercooled rim 27 of the inner door closes is `also watercooled, being supplied with water in the usual manner by pipes not shown. A casing 33 forms an inner door receiving chamber which, when the inner door 22 is in the closed position, is vented by open communication with the heating chamber 10 of the furnace. The frame 32 is spaced from the refractory wall of the furnace chamber to provide a passage therebetweenl for the raising and lowering of the door.

The inner door may be raised to open it, as in Fig. 2, or may be lowered to open it Aas in Fig. 3. When the inner door 22 is closed, the furnace atmosphere will ordinarily vent through a bypass pipe 34 from the furnace heating chamber 10 to the charge vestibule 11. The rate of flow may be controlled by valve 35 in the bypass pipe.

To charge work to be heated into the furnace the outer door 21 is raised while the inner door 22 is kept closed. The atmosphere gas in the charge vestibule will, of course, be contaminated by air, and if inflammable will ordinarily be ignited automatically by pilots, not shown, as the outer door 21 is opened. After a box, or tray, of work W is charged into the vestibule, the outer'door is closed and furnace atmosphere gas entering the vestibule through pipe 34 purges the vestibule. Additional purge gas is delivered to the vestibule through pipe 36 on the top of the vestibule and between access covers 37 which are sealed by a trough 38 filled by sand (chrome ore) or oil. The purge gas may escape from the charge vestibule by leakage Iaround the outer door 21 or through a similar, specially provided vent pipe not shown. After the vestibule has been purged to the desired degree the inner door is opened and the basket or tray of work W is then advanced into the heating chamber 10 and the inner door 22 closed behind it. To avoid excessive leakage of atmosphere gas through the inner door when closed, a wedge 41 on the furnace wall shown in broken lines acts 0n a roller 42 on the door, also in broken lines, to hold the door tight against the frame 32 when in closed position.

It will be appreciated that the reduction of volume of the vestibule chamber by Venting the inner door receiving chamber to the furnace rather than to the vestibule is considerable, and results in reduction of the time and ow of purge gas necessary to purge the vestibule to a given condition. By venting the door receiving chamber to the furnace the gas therein may be hotter when the door is closed, thus less gas will be in the space due to its expanded volume than would be the case if the space were vented to the cold vestibule; thus that gas does not expand so much when the hot-faced inner door moves into it, 'and variations of furnace pressure are reduced when the door is opened at ya given rate of speed. It is accordingly possible to automatically open that door faster without blowing Iatmosphere rthrough Vgas seals such as in the trough`3`8 of the vestibule, and theldoor may bel closed faster with a given input of atmosphere gas tothe -furnace without danger of inltration of atmospheric air as hot furnace gas enters the -cold chamberwhenv the door is moved out. A l

Since the total Yeffective volume of the vestibule is reduced, the volume o'fgas required tofpurge it to the same degree after opening theouter door is reduced, and since total contaminants from the vestibule are a product of volume and Vconcentration of impurities, it is no longer necessary -to purge the vestibule to the same degree of purity of vestibule .gas before opening the inner door. This, of course, results in fasterpossible pushing cycles on automatic furnaces than possible with prior inner door designs. Alternatively, much closer control of furnace atmosphere is possible with the same gas flows in purging the vestibule due to less contamination of furnace vatmosphere from air, thus making .possible adequate and practical operationalL control of Asuch delicate processes as surface carbon restoration, carburization with less than the normal maximum surface carbon in the carburized case, and thelike. n

Having described my invention, l claim:

1. Furnace structure comprising, in combination, `gas tight wall means forming a refractory lined'heating chamber having an access opening thereto, a vestibule forming a chamber alignedwwith said opening, and a door receiving chamber between the heating'chamber and the vestibule chamber -at the opening; an outer door for the vestibule; a refractory lined door in the door receiving chamber having 'a rim facing the vestibule when in a closed position; and a door frame on the vestibule facing and adapted to receive the rim when the refractory 'lined door is in Yclosed position, whereby to seal the gas in the vestibule from the gas in the door chamber `and the heating chamber. i

2. Furnace structure-according to claim 1 wherein the door frame and the rim are internally cooled metal, and comprising a by-pass pipe connecting the heating chamber with the vestibule chamber for passage therethrough of gas from one of said chambers to the other.

3. In ean atmosphere furnace comprising wall means forming a heating chamber, a vestibule therefor, a door chamber therebetween `in which an inner door moves to close or open van access opening between the heating chamber and the vestibule, and an outer door for the vestibule, the improvement which'comprises an inner door, a door frame on the vvestibule for the inner door, and a rim on the inner door for sealing against the door frame whereby to seal the atmosphere in the vestibule from the atmosphere in the heating chamber and the door chamber.

4. The improvement-according to claim 3 wherein the rim and the door frame are internally cooled and flat to form a substantially gas' tight seal when the door is closed, and the inner door is A"re'fr'actczr'ylined toform with the refractory lining of the heating chamber a heat Seal to prevent overheating of the'rim and the lframe when the inner door is closed.

5. Furnace structnrecomprising, in'combination, gas tight wall means forming a heating chamber, having an access opening thereto, a vestibule forming a chamber aligned with `said opening, -and -a door receiving chamber between the heating chamber and the vestibule chamber at the opening; an outer door -for `the vestibule; an inner door in the door receivingchamberl having a rim facing the vestibule when ina closedy position; a door frame 'on the vestibule facing and-adapted to` receive the rim when the inner door is in closed position; meansvfor moving said inner door into said door receiving chamber; and means to deliver gas 'to said vestibule to purge the same whereby the vestibule chamber may be purged with gas while said inner door seals the same from the door receiving chamber.

References Cited -in'fthe tile of this patent y UNITED STATES PATENTS 132,974 Miles Nov. 12, 1872 687,304 Grendel Nov. 26, 1901 748,457 Am'i'no'iV Dec. 29, 1903 1,102,197 Knox June 30, 1914 1,103,297 Knox July 14, 1914 1,261,555 Knox Apr. 2, 1918 1,351,914 "Knox Sept. 7, 1920 1,503,465 Amsler Ang.Y 5, 1924 1,680,365 Cort et al Aug. 14, 1928 1,818,759 Schrur'm Aug. 11, 1931 2,208,705 Soubbotin'et al Ily 23, 1940 2,435,318 McPeaters "Feb, 3, l11948 FOREIGN PATENTS' 442,355 'Germany Mar. 30, 19'27 

